Support mechanism and feeding unit including same

ABSTRACT

A supporting mechanism for movably supporting a member to be supported along a supporting shaft, comprises supporting members and a pressing device. The supporting members are provided on the member to be supported. Each of the supporting members comes into contact with the supporting shaft on at least two contact points so as to be movable on the supporting shaft. The at least two contact points are apart from each other. The pressing device presses the supporting members against the supporting shaft so that the contact points of each supporting member simultaneously come into contact with the supporting shaft.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a support mechanism and afeeding unit including such a mechanism, and more specifically to asupport mechanism, which moves a pickup for optically writing andreading information on and from a recording surface of a recordingmedium, along the recording surface thereof, while supporting thepickup, as well as a feeding unit including such a support mechanism.

[0003] 2. Discussion of the Background

[0004] In recent years, optical discs including CDs (Compact Discs),DVDs (Digital Video Discs), and MDs (Mini Discs) have been put intopractical use as information recording media onto or from whichinformation is written and read utilizing an optical beam such as alaser beam.

[0005] A device, which is known as a pickup, is used to radiate anoptical beam onto an information-recording surface of the optical discand receive the light reflected from the surface. While the pickup ismoved in parallel with the information-recording surface in the radialdirection of the optical disc, the optical disc rotates. This rotationenables bits of information to optically be written or read onto or frominformation trucks formed spirally on the optical disc.

[0006] Referring to FIGS. 13 to 16, a conventional feeding unit formoving the pickup in the radial direction of the optical disc inparallel with the information-recording surface will now be described.

[0007]FIG. 13 is a plan view illustrating the conventional feeding unit,FIG. 14 is a cross-sectional view cut along the line XIV-XIV in FIG. 13(or FIG. 15) and FIG. 15 is a bottom view illustrating the conventionalfeeding unit. FIG. 16 is an enlarged cross-sectional view of asupporting mechanism included in the conventional feeding unit.

[0008] As shown in FIGS. 13 to 15, the conventional feeding unit S′includes a pickup casing 100 on which a pickup 100 a is secured. Thepickup 100 a has a lens 101 and various drive parts. The lens 101 isused to radiate an optical beam B and receive light that is reflected onan optical disc DK. The drive parts drive optical parts, such as asemiconductor laser, and the lens 101, both of which produce the opticalbeam B cooperatively, in the trucking or focus direction of the opticaldisc DK.

[0009] The pickup casing 100 has two sides facing to each other. On oneside thereof, two main support members 102 are mounted so as to protrudefrom the side. On the other side thereof, one sub support member 105 ismounted.

[0010] A through hole is formed through each of the two main supportmembers 102 that allow a main shaft 103, which is secured by a not-shownchassis or others, to move through the through holes in the directionparallel with the direction of movement of the pickup casing 100. Themain shaft 103 passing through the through holes permits the one side ofthe pickup casing 100 to be supported movably.

[0011] On the other hand, the sub support member 105 is formed so thatit is able to pinch a sub shaft 106 secured by a not-shown chassis orother members in the direction parallel with the main shaft 103. The subsupport member 105 receives the sub shaft 106. This receipt enables theother side of the pickup casing 100 to be supported movably by the subshaft 106.

[0012] On the outer circumferential surface of the main shaft 103, afeeding screw 103 a is made in the form of a helical to move the pickupcasing 100 along the feeding screw. A rack gear 111 engaging with thefeeding screw 103 a is provided at the tip of a pressing spring 112secured at the bottom of the pickup casing 100 with the help of a screw113.

[0013] The pressing spring 112 presses the rack gear 111 in a pressingdirection shown by an arrow in FIG. 16. This makes it possible that therack gear 111 engages with the feeding screw 103 a.

[0014] In the conventional feeding unit S′, the main shaft 103 is drivento rotate by an electric motor not shown, with the result that the rackgear 111 engaging with the feeding screw 103 a travels along the mainshaft 103. Concurrently with this travel, the sub support member 105travels along the sub shaft 106, which allows the pickup casing 100itself to move in the radial direction of the optical disk DK togetherwith the pickup 100 a.

[0015] When the pickup casing 100 moves, delayed movement of the subsupport member 105 relative to the movement of the rack gear 111 occursdue to friction between the sub shaft 106 and the surface of the subsupport member 105, which comes into contact with the sub shaft 106. Insuch a case, force having a function of turning clockwise orcounterclockwise the pickup casing 100 in FIGS. 13 and 15 is applied tothe pickup casing 100. The two main support members 102 are provided soas to be apart from each other, with the result that the pickup casing100 is supported on the main shaft 103. In addition, a resilient forceis applied to the region of the main shaft 103 between the two mainsupport members 102 by means of the pressing spring 112. It is thereforepossible to prevent the pickup casing 100 from turning clockwise orcounterclockwise in FIGS. 13 and 15.

[0016] Further, in the conventional feeding unit S′, in order to ensurea smooth movement of the pickup casing 100 with backlash of the pickupcasing 100 restricted to a minimum, it is required that the throughholes of the main support members 102 (through which the main shaft 103passes) be worked with precision in relation to the diameter or otherfactors of the main shaft 103.

[0017] To realize such a higher precision, as shown in FIGS. 13 to 16,the conventional feeding unit S′ adopts a metal bush 110 tightlyinserted into the through hole of each main support member 102. Then,working of a sizing treatment is performed to raise the precision of acoaxial degree to the main shaft 103. Alternatively, the through holesare subjected to the finishing treatment of the through holes, which isconducted as the secondary finishing treatment. In addition, in the casethat the main support members 102 are formed of resin, it is required touse a mold produced with precision. Even when any finishing treatment isused, it is required that the through holes be formed under severequality control.

[0018] However, the conventional feeding unit S′ having theabove-described structure provides higher costs for the parts, becauseit is required that the inner surface of each through hole be formedwith a high precision. In addition, in cases where suspended dusts gointo the through hole and remain in a gap between the main shaft 103 andthe through hole (see FIG. 16), it may be difficult for the pickupcasing 100 to move smoothly.

SUMMARY OF THE INVENTION

[0019] An object of the present invention, which was made in view of theabove-mentioned problems, is to provide a support mechanism that permitsto decrease its manufacturing cost, minimize influences of dusts orothers put on the main shaft on the movement of the pickup casing, andreduce frictional resistance generated between the main support memberand the main shaft, leading to a smooth movement of the pickup casing,as well as to provide a feeding unit for a pickup casing, which includessuch a support mechanism.

[0020] In order to realize the above object, the supporting mechanism ofthe present invention for movably supporting a member to be supportedalong a supporting shaft, comprises:

[0021] a plurality of supporting members provided on the member, each ofsaid supporting members contacting with the supporting shaft on at leasttwo contact points so as to be movable on the supporting shaft, the atleast two contact points being apart from each other; and

[0022] a pressing device for pressing the plurality of supportingmembers against the supporting shaft so that the contact points of eachsupporting member simultaneously come into contact with the supportingshaft.

[0023] Accordingly, the pressing device presses the plurality ofsupporting members against the supporting shaft so that the contactpoints of each supporting member simultaneously come into contact withthe supporting shaft. All the contact points of each supporting membercome into contact with the supporting shaft simultaneously and all ofthe plural supporting members come into contact with the supportingshaft simultaneously on the contact points. Hence, with the supportingmembers pressed on only the plurality of points as they contact thesupporting shaft, the supporting members still hold the member in astable manner. It is unnecessary to form the whole bodies of thesupporting members with a high precision, which helps to reduce amanufacturing cost of the feeding unit itself. Additionally, even whendusts come onto the supporting shaft, influence of such dusts on themovement of the member can be minimized. Furthermore, a frictionalresistance caused between the supporting members and the supportingshaft can be reduced remarkably to provide a smooth movement of themember to be supported.

[0024] Preferably, the supporting member has two contact surfaces, whichinclude the contact points, respectively and are in parallel with thesupporting shaft, and the pressing device comes into contact with thesupporting shaft at a position existing between the supporting membersin a parallel direction with the supporting shaft to press thesupporting shaft.

[0025] Accordingly, the supporting members come into contact with thesupporting shaft through the two contact surfaces and the pressingdevice presses each supporting member against the supporting shaft in aplace between the supporting members in the parallel direction with thesupporting shaft. This makes it possible to movably support the memberin a more stable manner.

[0026] It is also preferred that the supporting shaft has an outercircumferential surface on which a threaded portion is formed to movethe member to be supported, and the pressing device is fixed to themember to be supported and includes a rack gear engaging with thethreaded portion so as to move the member along the supporting shaft.

[0027] Thus, the pressing device fixed to the member allows the rackgear to be pressed and engaged against and with the threaded portionformed on the supporting shaft. It is therefore possible to support themember to be supported and move it smoothly along the supporting shaft.

[0028] It is also preferred that the supporting mechanism furthercomprises a feeding shaft being disposed in parallel with the supportingshaft and having an outer circumferential surface on which a threadedportion is formed to move the member to be supported, and ischaracterized in that the pressing device is fixed to the member to besupported and includes a rack gear engaging with the threaded portion soas to move the member along the supporting shaft.

[0029] Thus, the feeding shaft is provided on its outer circumferentialsurface with the threaded portion. In addition, the pressing device isfixed to the member to be supported and includes the rack gear engagingwith the threaded portion. It is therefore possible to support themember to be supported and move it smoothly along the supporting shaft.

[0030] In the supporting mechanism of the present invention, the atleast two contact points may be apart from each other in acircumferential direction of the supporting shaft.

[0031] The present invention also provides a feeding unit comprising:

[0032] (a) a supporting mechanism for movably supporting a member to besupported along a supporting shaft, comprising:

[0033] a plurality of supporting members provided on the member, each ofsaid supporting members contacting with the supporting shaft on at leasttwo contact points so as to be movable on the supporting shaft, the atleast two contact points being apart from each other, said supportingshaft having an outer circumferential surface on which a threadedportion is formed to move the member to be supported; and

[0034] a pressing device for pressing the plurality of supportingmembers against the supporting shaft so that the contact points of eachsupporting member simultaneously come into contact with the supportingshaft and the plurality of supporting members simultaneously come intocontact with the supporting shaft, said pressing device being fixed tothe member to be supported and includes a rack gear engaging with thethreaded portion so as to move the member along the supporting shaft;and

[0035] (b) a rotation device for rotating the threaded portion engagingwith the rack gear, thereby moving the member to be supported along thesupporting shaft.

[0036] In such a feeding unit, the pressing device may come into contactwith the supporting shaft at a position existing between the supportingmembers in a parallel direction with the supporting shaft to press thesupporting shaft.

[0037] The present invention also provides a feeding unit comprising:

[0038] (a) a supporting mechanism for movably supporting a member to besupported along a supporting shaft, comprising:

[0039] a plurality of supporting members provided on the member, each ofsaid supporting members contacting with the supporting shaft on at leasttwo contact points so as to be movable on the supporting shaft, the atleast two contact points being apart from each other,

[0040] a pressing device for pressing the plurality of supportingmembers against the supporting shaft so that the contact points of eachsupporting member simultaneously come into contact with the supportingshaft and the plurality of supporting members simultaneously come intocontact with the supporting shaft, the pressing device being fixed tothe member to be supported and including a rack gear engaging with thethreaded portion so as to move the member along the supporting shaft;and

[0041] a feeding shaft being disposed in parallel with the supportingshaft and having an outer circumferential surface on which a threadedportion is formed to move the member to be supported; and

[0042] (b) a rotation device for rotating the threaded portion engagingwith the rack gear, thereby moving the member to be supported along thesupporting shaft.

[0043] In such a feeding unit, the supporting member may have twocontact surfaces, which include the contact points, respectively and arein parallel with the supporting shaft, and the pressing device may comeinto contact with the supporting shaft at a position existing betweenthe supporting members in a parallel direction with the supporting shaftto press the supporting shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In the accompanying drawings:

[0045]FIG. 1 is a plan view illustrating a feeding unit of the firstembodiment of the present invention;

[0046]FIG. 2 is a cross-sectional view cut along the line II-II in FIG.2;

[0047]FIG. 3 is a bottom view of the feeding unit as shown in FIG. 1;

[0048]FIG. 4 is an enlarged cross-sectional view illustrating thefeeding unit of the first embodiment of the present invention;

[0049]FIG. 5 is a plan view illustrating the feeding unit of the secondembodiment of the present invention;

[0050]FIG. 6 is a cross-sectional view cut along the line VI-VI in FIG.5;

[0051]FIG. 7 is a bottom view of the feeding unit as shown in FIG. 5;

[0052]FIG. 8 is an enlarged cross-sectional view illustrating thefeeding unit of the second embodiment of the present invention;

[0053]FIG. 9 is a plan view illustrating the feeding unit of the thirdembodiment of the present invention;

[0054]FIG. 10 is a side view of the feeding unit as shown in FIG. 9;

[0055]FIG. 11 is a bottom view of the feeding unit as shown in FIG. 9;

[0056]FIG. 12 is an enlarged cross-sectional view illustrating thefeeding unit of the third embodiment of the present invention;

[0057]FIG. 13 is a plan view illustrating the conventional feeding unit;

[0058]FIG. 14 is a cross-sectional view cut along the line XIV-XIV inFIG. 13;

[0059]FIG. 15 is a bottom view of the conventional feeding unit as shownin FIG. 13; and

[0060]FIG. 16 is an enlarged cross-sectional view illustrating theconventional feeding unit.

PREFERRED EMBODIMENTS OF THE INVENTION

[0061] Various embodiments of the present invention will now bedescribed with reference to the accompanying drawings.

[0062] Each embodiment will now be described about a configuration inwhich the present invention is applied to a feeding unit for moving apickup optically reading and writing information from and onto anoptical disc. The feeding unit is constructed to move the pickup inparallel with an information-recording surface of the optical disc in aradial direction of the surface.

[0063] [First Embodiment]

[0064] The first embodiment of the present invention will now bedescribed with reference to FIGS. 1 to 4.

[0065]FIG. 1 is a plan view illustrating the feeding unit of the firstembodiment of the present invention, FIG. 2 is a cross-sectional viewcut along the line II-II in FIG. 2, FIG. 3 is a bottom view of thefeeding unit as shown in FIG. 1, and FIG. 4 is an enlargedcross-sectional view of the feeding unit of the first embodiment of thepresent invention, illustrating the main shaft 103 and its peripheralcomponents.

[0066] As shown in FIGS. 1 to 3, the feeding unit S1 includes a pickupcasing 100 on which a member, i.e., a pickup 100 a to be supported issecured. The pickup 100 a has a lens 101 and various drive parts. Thelens 101 is used to not only radiate an optical beam B but also receivelight that reflected on an optical disc DK. The drive parts driveoptical parts, such as a semiconductor laser, and the lens 101, both ofwhich produce the optical beam B cooperatively, in the trucking or focusdirection of the optical disc DK.

[0067] The pickup casing 100 has two sides facing to each other. On oneside thereof, two main support members 1 are provided so as to protrudefrom the side surface of the pickup casing 100. On the other sidethereof, one sub support member 105 is provided.

[0068] The feeding unit S1 of the first embodiment of the presentinvention differs from the conventional feeding unit S′ in structure andshape of (i) the main support members 1 serving as the supportingmembers, which are provided on the one of the opposite side surfaces ofthe pickup casing 100, i.e. the member to be supported, and (ii) apressing spring 2 serving as the pressing device.

[0069] The pressing spring 2 is formed into a leaf spring. The pressingspring 2 has a base end portion and a bent portion. The pressing spring2 is placed on the bottom of the pickup casing 100 so that itslongitudinal direction is perpendicular to the main shaft 103. In such astate, the base end portion of the pressing spring 2 is fixed to thebottom of the pickup casing 100 by means of a screw 113. The bentportion of the pressing spring 2 comes into contact with the main shaft103 and presses it so that the main shaft 103 is held between the mainsupport member 1 and the bent portion of the pressing spring 2.

[0070] A rack gear 111 is provided on the bent portion of the pressingspring 2 so as to engage with a threaded portion 103 a of the main shaft103. Rotation of the main shaft 103 therefore cause the pickup casing100 to move. The bent portion of the pressing spring 2 pushes the mainshaft 103 against the receiving surfaces 3 a and 3 b of the supportmember 1.

[0071] The main shaft 103 is located to pass through the two mainsupport members 1 and the pressing spring 2. On the outercircumferential surface of the main shaft 103, a threaded portion 103 ais formed in the helical pattern so as to engage with the rack gear 111.The main shaft 103 is driven by an electric motor 4, so that therotation of the main shaft 103 is transmitted to the rack gear 111.

[0072] On the other hand, the sub support member 105 is formed so as tobe capable of pinching a sub shaft 106 secured by a not-shown chassis orother members. The sub shaft 106 is directed in parallel with the mainshaft 103. This enables the other side of the pickup casing 100 to besupported movably by the sub shaft 106.

[0073] In the first embodiment, each of the two main support members 1has smooth receiving surfaces 3 a and 3 b, which are at right angles toeach other. The receiving surfaces 3 a and 3 b of the main supportmember 1 come into contact with the main shaft 103 so that the pickupcasing 100 can be supported.

[0074] More specifically, as shown in FIG. 2, the tip end of thepressing spring 2, on which the rack gear 111 is provided, is bent at aslight angle. Thus the pressing spring 2 is permitted to apply apressing force to the main shaft 103 in the directions shown by arrowsin FIG. 4. This force caused the main shaft 103 to contact with thereceiving surfaces 3 a and 3 b formed on each main support member 1,thereby producing component forces X and Z at each main support member1, as illustrated in FIG. 4. The reaction to the component forces X andZ causes each main support member 1 to be pressed against the main shaft103 at the same time. The one side of the pickup casing 100, on whichthe main support members 1 are provided, can be supported by the mainshaft 103 in such a manner that the pickup casing 100 is prohibited frommoving in any direction orthogonal to the movement thereof. Accordingly,no backlash will be caused in the pickup casing 100.

[0075] The threaded portion 103 a is formed in a helical pattern on theouter circumferential surface of the main shaft 103, like theconventional feeding unit. The rack gear 111 engaging with the threadedportion 103 a is pressed through a pressing force generated by thepressing spring 2, as shown in FIG. 4, with the result that the rackgear 111 tightly engages with the threaded portion 103 a. With both ofthe rack gear 111 and the threaded portion 103 a engaged therewith, themotor 4 is driven to move the pickup casing 100. Because the rack gear111 is forced to move along the main shaft 103, with the sub supportmember 105 allowed to freely travel along the sub shaft 106, the driveof the motor 4 causes the pickup casing 100 together with the pickup 100a to travel in the radial direction of the optical disc DK.

[0076] The travel of the pickup casing 100 also causes frictionresistance between the sub shaft 106 and a contact surface of the subsupport member 105 to the sub shaft 106. This resistance causes the subsupport member 105 to move later than the rack gear 111. Such a delaycauses a force having a function of turning the pickup casing 100 in theclockwise or counter clockwise direction in FIGS. 1 and 3. However, thetwo main support members 1 are disposed apart from each other in orderto support the pickup casing 100 on the main shaft 103 and the pressingspring 2 pushes a certain intermediate position of the main shaft 103existing between the two main support members 1. Such a structureprevents the pickup casing 100 from turning in the clockwise or counterclockwise direction.

[0077] As described above, the feeding unit SI of the first embodimentenables each main support member 1 to be pressed against the main shaft103. In this action, each of the plurality of main support members 1provided on the pickup casing 100 is brought into contact with the mainshaft 103 on at least two points, when the support members 1 move alongthe main shaft 103. These contact points are apart from each other inthe circumferential direction of the main shaft 103. All the contactpoints of each main support member 1 come into contact with the mainshaft 103 simultaneously and all the two main support members 1 comeinto contact with the main shaft 103 simultaneously on the contactpoints.

[0078] Accordingly, with the main support members 1 pressed on only thetwo points as they contact the main shaft 103, the main support members1 still hold the pickup casing 100 in a stable manner. It is unnecessaryto form the whole bodies of the main support members 1 with highprecision, which helps to reduce a manufacturing cost of the feedingunit itself. Additionally, even when dusts come onto the main shaft 103,influence of such dusts on the movement of the pickup casing 100 can beminimized. Furthermore, a frictional resistance caused between the mainsupport members 1 and the main shaft 103 can be reduced remarkably,providing a smooth movement of the pickup casing 100.

[0079] Each of the main support members 1 comes into contact with themain shaft 103 on the two receiving surfaces 3 a and 3 b. Additionally,the pressing spring 2 comes into contact with the main shaft 103 at agiven position between the main support members 1, which causes eachmain support member 1 to be pressed steadily against the main shaft 103.As a result, the pickup casing 100 can be supported with more stability.

[0080] In addition, one end of the pressing spring 2 is secured on thepickup casing 100, and the rack gear 111 is provided on the other end ofthe spring 2. The rack gear 111 engages with the threaded portion formedon the outer circumferential surface of the main shaft 103. Thisstructure makes it possible to smoothly move the pickup casing 100 alongthe main shaft 103, while still being supported.

[0081] [Second Embodiment]

[0082] The second embodiment of the present invention will now bedescribed with reference to FIGS. 5 to 8.

[0083]FIG. 5 is a plan view illustrating the feeding unit of the secondembodiment of the present invention, FIG. 6 is a cross-sectional viewcut along the line VI-VI in FIG. 5, FIG. 7 is a bottom view of thefeeding unit as shown in FIG. 5, and FIG. 8 is an enlargedcross-sectional view illustrating the feeding unit of the secondembodiment of the present invention, illustrating the main shaft 13 andits peripheral components.

[0084] In the second embodiment, the same reference numerals are givento the same structural components as those in the first embodiment asshown in FIGS. 1 to 4 as well as in the conventional feeding unit asshown in FIGS. 13 to 16, and detailed explanation thereof will thereforebe omitted.

[0085] The feeding unit S2 of the second embodiment differs from theconventional feeding unit S′ in the following configurations. Thefeeding unit S2 is provided with main support members 10 and thepressing spring 11, both of which are arranged on the one side of thepickup casing 100 and are different in construction and shape from thosein the first embodiment. In addition, unlike the conventional feedingunit S′, the main shaft 13 for supporting the pickup casing 100 isprovided independently from the feeding shaft 12 on which the threadedportion 12 a is formed.

[0086] As shown in FIGS. 5 to 7, to support the pickup casing 100, thefeeding unit S2 of the second embodiment adopts the sub shaft 106 andthe main shaft 13, which is formed into a cylindrical rod-shape with nothreaded portion and arranged in parallel with the sub shaft 106. Inorder to move the pickup casing 100 in parallel with theinformation-recording surface of an optical disk DK in the radialdirection thereof, the feeding shaft 12 is additionally disposed at anoutward position beyond the main shaft 13, when viewed from the pickupcasing 100, but still parallel with the main shaft 13. On the outercircumferential surface of the feeding shaft 12, a threaded portion 12 ais formed to move the pickup casing 100.

[0087] On one of the opposite sides of the pickup casing 100 of thesecond embodiment, two main support members 10 are provided so as to beapart from each other. The main support members 10 come into contactwith the main shaft 13 so as to movably support the pickup casing 100 inparallel with the information-recording surface in the radial directionof the optical disc DK. On the other side thereof, the sub supportmember 105 is provided so as to come into contact with the sub shaft106. The sub support member 105 also movably supports the pickup casing100.

[0088] Flat receiving surfaces 3 a and 3 b are formed respectively oneach main support member 10 so as to be right angles to each other inthe same manner as the main support members 1 described in the firstembodiment. The receiving surfaces 3 a and 3 b come into contact withthe main shaft 13 to support the pickup casing 100.

[0089] The pressing spring 11 has a length extending from the side edgeof the pickup casing 100 on the side of the main shaft 13 to thethreaded portion 12. On the tip end of the pressing spring 11, a rackgear 111 is provided to engage with the threaded portion 12 a to movethe pickup casing 100. Furthermore, the tip end of the rack gear 111 isbent so as to press the feeding shaft 12 in the directions shown byarrows in FIG. 8.

[0090] The other ends of the pressing spring 11 are fixed on the pickupcasing 100 by screws 113 a and 113 b. As a result, two forces, which areequal in strength to two component forces of a pressing force caused bythe pressing spring 11 to the feeding shaft 12 through the rack gear111, as shown in FIG. 8, are applied to the main shaft 13 at each mainsupport member 10. The reaction to the two component forces applied tothe main shaft 13 causes each main support member 10 to be pressedagainst the main shaft 13 at the same time. The one side of the pickupcasing 100, on which the main support members 10 are provided, can besupported by the main shaft 13 such that the pickup casing 100 isprohibited from moving in any direction orthogonal to the movementthereof. Accordingly, no backlash will be caused in the pickup casing100.

[0091] The threaded portion 12 a for moving the pickup casing 100 isformed into a helical pattern on the outer circumferential surface ofthe feeding shaft 12, as described above. The rack gear 111 engagingwith the threaded portion 12 a is pressed by a pressing force generatedby the pressing spring 2, as shown in FIG. 8, with the result that therack gear 111 tightly engages with the threaded portion 12 a. The rackgear 111 and the threaded portion 12 a engage with each other. Anot-shown motor is driven to move the pickup casing 100. Because therack gear 111 is forced to move along the feeding shaft 12 together withthe sub support member 105 allowed to freely travel along the sub shaft106, the drive of the motor causes the pickup casing 100 together withthe pickup 100 a to travel in the radial direction of the optical discDK.

[0092] The travel of the pickup casing 100 causes a frictionalresistance between the sub shaft 106 and the contact surface of the subsupport member 105 coming into contact thereto in the same manner as thefirst embodiment of the present invention. This resistance causes thesub support member 105 to move later than the rack gear 111. Such adelay causes a force having a function of turning the pickup casing 100in the clockwise or counter clockwise direction in FIGS. 5 to 7.However, the two main support members 10 are disposed apart from eachother in order to support the pickup casing 100 on the main shaft 13 andthe pressing spring 11 pushes a certain intermediate position of themain shaft 13 existing between the two main support members 10. Such astructure prevents the pickup casing 100 from turning in the clockwiseor counter clockwise direction.

[0093] As described above, the feeding unit S2 of the second embodimentenables each main support member 10 to be pressed against the main shaft13. In this action, each of the plurality of main support members 10provided on the pickup casing 100 is brought into contact with the mainshaft 13 on at least two points, when the support members 10 move alongthe main shaft 13. All the contact points of each main support member 10come into contact with the main shaft 13 simultaneously and all the twomain support members 10 come into contact with the main shaft 13simultaneously on the contact points.

[0094] Accordingly, with the main support members 10 pressed on only thetwo points as they contact the main shaft 13, the main support members10 still hold the pickup casing 100 with a stable manner. It isunnecessary to form the whole bodies of the main support members 10 withhigh precision, which helps to reduce a manufacturing cost of thefeeding unit itself. Additionally, even when dusts come onto the mainshaft 13, influence of such dusts on the movement of the pickup casing100 can be minimized. Furthermore, a frictional resistance causedbetween the main support members 10 and the main shaft 13 can be reducedremarkably, providing a smooth movement of the pickup casing 100.

[0095] Each of the main support members 10 comes into contact with themain shaft 13 on the two receiving surfaces 3 a and 3 b. Additionally,the pressing spring 11 comes into contact with the feeding shaft 12 at aprescribed position between the main support members 10. This causeseach main support member 10 to be pressed steadily against the mainshaft 13. As a result, the pickup casing 100 can be supported with morestability.

[0096] In addition, one end of the pressing spring 11 is secured on thepickup casing 100, and the rack gear 111 is provided on the other end ofthe spring 11. The rack gear 111 engages with the threaded portion 12 aformed on the outer circumferential surface of the feeding shaft 12disposed in parallel with the main shaft 13. This structure makes itpossible to smoothly move the pickup casing 100 along the main shaft 13,while still being supported.

[0097] [Third Embodiment]

[0098] The third embodiment of the present invention will now bedescribed with reference to FIGS. 9 to 12.

[0099]FIG. 9 is a plan view illustrating the feeding unit of the thirdembodiment of the present invention, FIG. 10 is a side view of thefeeding unit as shown in FIG. 9, FIG. 11 is a bottom view of the feedingunit as shown in FIG. 9, and FIG. 12 is an enlarged cross-sectional viewillustrating the feeding unit of the third embodiment of the presentinvention, illustrating the main shaft 103 and its peripheralcomponents.

[0100] In the third embodiment, the same reference numerals are given tothe same structural components as those in the first embodiment as shownin FIGS. 1 to 4 as well as in the conventional feeding unit as shown inFIGS. 13 to 16, and detailed explanation thereof will therefore beomitted.

[0101] The feeding unit S3 of the third embodiment differs from theconventional feeding unit S′ in the arrangement of both of the sub shaft106 and the main shaft 103 for supporting the pickup casing 100. Morespecifically, both of the sub shaft 106 and the main shaft 103 arearranged so as to pass below the pickup casing 100 when viewing from thetop. Therefore, the pickup casing 100 is moved so as to bridge a spacebetween the shafts 106 and 103.

[0102] As shown in FIGS. 9 to 11, in the feeding unit S3 of the thirdembodiment, a recess 23, which is rectangular in section with its oneside opened, is formed along one end of the bottom of the pickup casing100. The size of the recess 23 is determined so that the recess 23exactly receives the sub shaft 106 to support the pickup casing 100. Areceiving surface 21 a is formed along one wall of the recess 23 andcomes into contact with the sub shaft 106 when the recess 23 receivesthe sub shaft 106. A sub support member 21 is fixed on the bottom so asto cover the lower opening of the recess 23. Thus, the sub shaft 106 canbe held between the receiving surface 21 a and the sub support member21, resulting in that one side end of the pickup casing 100 is movablysupported along the sub shaft 106.

[0103] On the other hand, on the bottom of the pickup casing 100, tworecesses 22 are further formed so as to be apart from each other atprescribed positions along a groove on the opposite side to theabove-mentioned recess 23. The recesses 22 are used to receive the mainshaft 103. Each recess 22 is formed in section into a reversed V-shape,so receiving surfaces 22 a and 22 b capable of contacting with the mainshaft 103 are formed on the walls of each recess 22, respectively. Apressing spring 20 is secured on the bottom of the pickup casing 100.The one end of the pressing spring 20 is located at a center between therecesses 22. Therefore, pinching the main shaft 103 between the recesses22 (i.e., the receiving surfaces 22 a and 22 b of each recess 22) andthe one end of the pressing spring 20 permits the other side end of thepickup casing 100 to be supported movably.

[0104] On the outer circumferential surface of the main shaft 103, athreaded portion 103 a is formed to move the pickup casing 100 inparallel with the information-recording surface in the radial directionof an optical disc DK.

[0105] The other ends of the pressing spring 20 are fixed on the bottomof the pickup casing 100 by screws 113 a and 113 b. A rack gear 111 isprovided on the tip end of the pressing spring 20 to move the pickupcasing 100 by engaging with the threaded portion 103 a. As shown in FIG.12, the pressing spring 20 has a shape so as to press at its end themain shaft 103 in the direction of a pressing force indicated by arrows.

[0106] The pressing force permits the main shaft 103 to contact with thereceiving surfaces 22 a and 22 b of each recess 22 simultaneously,generating two component forces as shown in FIG. 12. The reaction to thetwo component forces causes the receiving surfaces 22 a and 22 b of eachrecess 22 to be pressed against the main shaft 103 at the same time. Themain shaft 103 can support the pickup casing 100, while preventing thepickup casing 100 from moving in any direction orthogonal to themovement thereof. Accordingly, no backlash will be caused in the pickupcasing 100.

[0107] The threaded portion 103 a for moving the pickup casing 100 isformed in a helical pattern on the outer circumferential surface of themain shaft 103, as described above. The rack gear 111 engaging with thethreaded portion 103 a is pressed by a pressing force generated by thepressing spring 20, as shown in FIG. 12, with the result that the rackgear 111 tightly engage s with the threaded portion 103 a. The rack gear111 and the threaded portion 103 a engaged with each other. A not-shownmotor is driven to move the main shaft 103. Because the rack gear 111 isforced to move along the main shaft 103 with the sub support member 21allowed to freely travel along the sub shaft 106, the drive of the motorcauses the pickup casing 100 together with the pickup 100 a to travel inthe radial direction of the optical disc DK.

[0108] The travel of the pickup casing 100 causes a frictionalresistance between the sub shaft 106 and the contact surface of the subsupport member 21 coming into contact thereto. This resistance causesthe sub support member 21 to move later than the rack gear 111. Such adelay causes a force having a function of turning the pickup casing 100in the clockwise or counter clockwise direction in FIGS. 9 to 11.However, the two recesses 22 (the two sets of receiving surfaces 22 aand 22 b) are disposed apart from each other in order to support thepickup casing 100 on the main shaft 103 and the pressing spring 20pushes a certain intermediate region of the main shaft 103 existingbetween the two recesses 22. Such a structure prevents the pickup casing100 from turning in the clockwise or counter clockwise direction.

[0109] As described above, the feeding unit S3 of the third embodimentenables each recess 22 to be pressed against the main shaft 103. In thisaction, each of the plurality of recesses 22 formed on the pickup casing100 is brought into contact with the main shaft 103 on at least twopoints, when the pickup casing 100 moves along the main shaft 103. Allthe contact points of each recess 22 come into contact with the mainshaft 103 simultaneously and all the two recesses 22 come into contactwith the main shaft 103 simultaneously on the contact points.

[0110] Accordingly, with the recesses 22 pressed on only the two pointsas they contact the main shaft 103, the recesses 22 still hold thepickup casing 100 with a stable manner. It is unnecessary to form thewhole bodies of the recesses 22 with high precision, which helps toreduce a manufacturing cost of the feeding unit itself. Additionally,even when dusts come onto the main shaft 103, influence of such dusts onthe movement of the pickup casing 100 can be minimized. Furthermore, africtional resistance caused between the recesses 22 and the main shaft103 can be reduced remarkably to gain a smooth movement of the pickupcasing 100.

[0111] Each of the recesses 22 is in contact with the main shaft 103 onthe two receiving surfaces 22 a and 22 b. Additionally, the pressingspring 20 comes in contact with the main shaft 103 at a prescribedposition between the recesses 22. This causes each recess 22 to bepressed steadily against the main shaft 103. As a result, the pickupcasing 100 can be supported with more stability.

[0112] In addition, the one end of the pressing spring 20 is fixed onthe pickup casing 100, and the rack gear 111 is provided on the otherend of the spring 20. The rack gear 111 engages with the threadedportion 103 a that is formed on the outer circumferential surface of themain shaft 103. This structure makes it possible to smoothly move thepickup casing 100 along the main shaft 103, while still being supported.

[0113] In the above-described embodiments, there is described thepresent invention, which is applied to the feeding unit including thepickup 100 a for optically writing and reading information. The presentinvention is not limited only to these embodiments, but may be appliedto a feeding unit including a pickup for electromagnetically writing andreading information.

[0114] The entire disclosure of Japanese Patent Application No.2001-24733 filed on Jan. 31, 2001 including the specification, claims,drawings and summary is incorporated herein by reference in itsentirety.

What is claimed is:
 1. A supporting mechanism for movably supporting amember to be supported along a supporting shaft, comprising: a pluralityof supporting members provided on the member to be supported, each ofsaid supporting members contacting with the supporting shaft on at leasttwo contact points so as to be movable on the supporting shaft, the atleast two contact points being apart from each other; and a pressingdevice for pressing the plurality of supporting members against thesupporting shaft so that the contact points of each supporting membersimultaneously come into contact with the supporting shaft.
 2. Thesupporting mechanism of claim 1, wherein the supporting member has twocontact surfaces, which include the contact points, respectively and arein parallel with the supporting shaft, and the pressing device comesinto contact with the supporting shaft at a position existing betweenthe supporting members in a parallel direction with the supporting shaftto press the supporting shaft.
 3. The supporting mechanism of claim 1,wherein the supporting shaft has an outer circumferential surface onwhich a threaded portion is formed to move the member to be supported,and the pressing device is fixed to the member to be supported andincludes a rack gear engaging with the threaded portion so as to movethe member along the supporting shaft.
 4. The supporting mechanism ofclaim 2, wherein the supporting shaft has an outer circumferentialsurface on which a threaded portion is formed to move the member to besupported, and the pressing device is fixed to the member to besupported and includes a rack gear engaging with the threaded portion soas to move the member along the supporting shaft.
 5. The supportingmechanism of claim 1, further comprising a feeding shaft being disposedin parallel with the supporting shaft and having an outercircumferential surface on which a threaded portion is formed to movethe member to be supported, wherein the pressing device is fixed to themember to be supported and includes a rack gear engaging with thethreaded portion so as to move the member along the supporting shaft. 6.The supporting mechanism of claim 2, further comprising a feeding shaftbeing disposed in parallel with the supporting shaft and having an outercircumferential surface on which a threaded portion is formed to movethe member to be supported, wherein the pressing device is fixed to themember to be supported and includes a rack gear engaging with thethreaded portion so as to move the member along the supporting shaft. 7.The supporting mechanism of claim 1, wherein the at least two contactpoints are apart from each other in a circumferential direction of thesupporting shaft.
 8. A feeding unit comprising: (a) a supportingmechanism for movably supporting a member to be supported along asupporting shaft, comprising: a plurality of supporting members providedon the member, each of said supporting members contacting with thesupporting shaft on at least two contact points so as to be movable onthe supporting shaft, the at least two contact points being apart fromeach other, said supporting shaft having an outer circumferentialsurface on which a threaded portion is formed to move the member to besupported; and a pressing device for pressing the plurality ofsupporting members against the supporting shaft so that the contactpoints of each supporting member simultaneously come into contact withthe supporting shaft and the plurality of supporting memberssimultaneously come into contact with the supporting shaft, saidpressing device being fixed to the member to be supported and includes arack gear engaging with the threaded portion so as to move the memberalong the supporting shaft; and (b) a rotation device for rotating thethreaded portion engaging with the rack gear, thereby moving the memberto be supported along the supporting shaft.
 9. The feeding unit of claim8, wherein the supporting member has two contact surfaces, which includethe contact points, respectively and are in parallel with the supportingshaft, and the pressing device comes into contact with the supportingshaft at a position existing between the supporting members in aparallel direction with the supporting shaft to press the supportingshaft.
 10. The supporting mechanism of claim 8, wherein the at least twocontact points are apart from each other in a circumferential directionof the supporting shaft.
 11. A feeding unit comprising: (a) a supportingmechanism for movably supporting a member to be supported along asupporting shaft, comprising: a plurality of supporting members providedon the member, each of said supporting members contacting with thesupporting shaft on at least two contact points so as to be movable onthe supporting shaft, the at least two contact points being apart fromeach other,; a pressing device for pressing the plurality of supportingmembers against the supporting shaft so that the contact points of eachsupporting member simultaneously come into contact with the supportingshaft and the plurality of supporting members simultaneously come intocontact with the supporting shaft, the pressing device being fixed tothe member to be supported and including a rack gear engaging with thethreaded portion so as to move the member along the supporting shaft;and a feeding shaft being disposed in parallel with the supporting shaftand having an outer circumferential surface on which a threaded portionis formed to move the member to be supported; and (b) a rotation devicefor rotating the threaded portion engaging with the rack gear, therebymoving the member to be supported along the supporting shaft.
 12. Thefeeding unit of claim 11, wherein the supporting member has two contactsurfaces, which include the contact points, respectively and are inparallel with the supporting shaft, and the pressing device comes intocontact with the supporting shaft at a position existing between thesupporting members in a parallel direction with the supporting shaft topress the supporting shaft.
 13. The supporting mechanism of claim 11,wherein the at least two contact points are apart from each other in acircumferential direction of the supporting shaft.